Her Majesty’s Nuclear Seaplane

She was a dazzling aircraft, a great winged hope of postwar Britain, the largest all-metal flying boat ever built. Her design incorporated brand-new technologies: a pressurized cabin, all-hydraulic controls and turboprop power. Yet even as she took to the skies over the 1953 Farnborough Air Show, the Saunders-Roe S.R.45 “Princess” was an anachronism built to serve a vanishing Empire.

Saunders-Roe, a firm with a long and distinguished history in seaplane design, responded to the Ministry of Supply’s 1945 request for a passenger flying boat to serve the postwar Transatlantic route.

The proposed seaplane’s range of more than 5,000 miles would also bring India and the Far East much closer to London. Following the May 1946 order for three planes, Saunders-Roe began construction at its Cowes plant on the Isle of Wight.

The huge aircraft — nearly as large as the legendary Spruce Goose — was to carry more than 100 passengers in cruise-liner style. Two decks, private cabins, lounges, dining rooms and staff quarters.

At the Farnborough Air Show that September, another Princess flyover amazed attendees, who would have been even more amazed had they known the plane lost hydraulic power and was kept flying level and straight by some keen piloting.

But though Princess Elizabeth ascended to the throne as Queen, the Princess did not become queen of the skies. Before the first aircraft was completed its intended customer, BOAC, decided that flying boats had no place in the company’s future. The RAF expressed interest in the three huge planes for transport use, but backed away as estimates of maintenance costs mounted.

The prospect of maintaining 10 engines along with fighting saltwater corrosion on the world’s biggest seaplane hull proved too rich for British aviation. Indeed, the British Empire began to die the year the Princess tender was offered in 1946, when an exhausted Britain turned to the U.S. to fight Communists in Greece, and the torch of rule passed west.

Now without a purpose, the one flying and two nearly-completed planes were placed in storage to await interest. And in 1956 interest came from a seaport on the other side of the world, from another country’s military.

The NB-36 didn’t actually fly on nuclear power. Rather it tested various shielding concepts for flight-crew protection. During a series of test flights over West Texas and New Mexico, the NB-36 was accompanied by a battalion of airborne Marines in case it crashed and the site had to be secured.

So when the U.S. Navy approached Convair with a really weird idea, the San Diego aircraft maker responded with alacrity. If the Princess flying boats were brought to America, asked the Navy, could Convair convert them to nuclear power? Yes, said the company, and drew up blueprints for the modifications. Like the Convair Crusader, the nuclear Princess would be a testbed for atomic-powered flight and crew shielding.

All that room prepared for Imperial dignitaries and posh travelers would accommodate a Pratt & Whitney liquid-metal-cooled reactor, a heat exchanger and some serious plumbing to run superheated (radioactive) air into special P&W gas turbines. The “hot” gas would replace gas heated by jet fuel once the big plane reached cruising altitude.